Weathermen warn that temperatures could soar to new highs between Friday and Tuesday, with the wet season not due to start until the third week of May.
Somkuan Tonjan, director of observation at the Meteorological Department, said on Wednesday morning that the heatwave would continue throughout Wednesday and Thursday under the influence of southerly and southeasterly winds.
From Friday through to Tuesday next week, he said, westerly and northwesterly winds would reach the North, Northeast, Central Plain and the East, with high temperatures that could break records set in 2016 and 2023.
A record 44.6°C was measured in Mae Hong Son province on April 28, 2016, and again in Tak province on April 15, 2023. Both provinces are in the North.
This year's high to date is 44.2°C, in the northern province of Lampang on Monday this week.
From May 1-3, westerly and southwesterly winds would arrive and signal a seasonal change. The wet season should then start in the third week of May, slightly later than normal, Mr Somkuan said.
Along with the extremely hot weather, demand for electricity set a new high on Monday night of 35,830 megawatts.
Dr Jurai Wongsawat, assistant director-general of the Department of Disease Control, said that 30 people had died of heat stroke in Thailand this year.
She advised people to avoid long exposure to strong sunlight and alcoholic beverages, regularly drink water and refrain from leaving anyone, especially children, inside vehicles parked outdoors.